A crucial factor when choosing a car is the type of drivetrain. Either used for an everyday commute to work in the city or for an offroad adventure on rough mountain terrains, the car's behavior and performance are tied up to its drivetrain and its capabilities. That's why it is very important for the driver to make a clear distinction between two of the most popular drivetrain types: AWD and 4WD.
The All-wheel drive system (known also as an AWD, for short) is known for powering simultaneously both front and rear wheels of the vehicle. However, AWD can be divided into two sub-types. The first one, called full-time AWD, continuously drives the vehicle's wheels. The other one, called part-time or automatic AWD, works as a 2WD during most of the time with the 4WD kicking in when the need for more traction control calls.
How exactly the All-wheel drive system works?No matter which sub-type of the All-wheel drive we have, neither one of them needs the driver's control over them in order to function properly. There are some modern systems that enable the person behind the wheel to control the power distribution between the wheels, but in the majority of cases, there's no need for such actions.
What's specific for the all-wheel drive is that the torque is distributed between each of the four wheels via a multitude of differential and viscous couplings or clutches – helping the traction optimization.
Let's get a look into the sub-types of the AWD.
The full-time AWD utilizes both front and rear axles continuously. It improves the vehicle's handling and performance equally on both - dry pavement and slippery road conditions.
The interesting side of this type of drivetrain is that it powers either the front or the rear wheels when working in normal conditions. When additional traction is needed, the other two wheels automatically tune in. That's possible thanks to a variety of electronic sensors, which detect, gather, process and directly send information to the drivetrain's computer.
The latter chooses when is the exact moment and what is the amount of power that needs to be transmitted to each of the four wheels.
The 4WD is probably one of the most popular and best-known types of drivetrains. It's commonly used in heavy-duty trucks and pickups (made for both offroad adventures and towing, and transportation of heavy objects). Typical for that kind of vehicles are the reinforced underbody, big-sized tires, tow hook, and higher ground clearance.
And just like the AWD system, the 4WD can also be divided into sub-types: part-time and full-time. Unlike the AWD, this drivetrain offers the driver control over the power distribution via an electric or mechanical lever.
The process is almost the same as in the AWD - power is continuously transmitted to each of the vehicle's wheels. However, depending on the machine's model and the drivetrain's design, the driver can control the way and the amount of power supplying the front and rear set of wheels.
Frequently used in huge SUVs and heavy-duty pickups, the part-time 4WD is ideal for extreme road and climate conditions. By default, the part-time 4WD utilizes either the front or the rear wheels. If the situation calls, the driver has the option to switch on all four wheels of the automobile. It's also possible for the driver to lock the differentials in order to maximize the traction in extreme offroad conditions.
There are two more sub-types of the 4WD, called a shift-on-the-fly and an automatic 4WD. The first one offers the driver the ability to switch between a 2WD to 4WD while the vehicle is still in motion. The second one reduces the fuel consumption thanks to electric sensors that gather information and transfer it to the system's computer that controls whether or not the 4WD is needed.